Stabilizer bars (also known as anti-roll bars and/or sway bars) are often used in motorized vehicles to at least partially couple the wheels of a single axle together to ensure stability and to ensure sufficient contact of the wheels with the road surface during cornering. In particular, during a hard turn or cornering, the weight of the vehicle shifts to the outer wheels, and the inner wheels may tend to carry less weight (thereby reducing traction with the road surfaces) or even lift off of the road surface. Stabilizer bars serve as a semi-rigid coupling between the wheels of an axle to urge the inner wheels downwardly and into contact with the road surface.
Active stabilization bar systems utilize a hydraulic system to drive the stabilizer bar when the vehicle system senses that actuation of the stabilizer bar will improve the handling performance of the vehicle. Existing hydraulic systems may include piston-driven systems to operate/actuate the stabilizer bar.
One type of stabilizer bar system has actuators for operating/actuating the stabilizer bar at both the front and rear axles. Different controlled pressures are applied or present in the front and rear actuators, which allows variable balancing therebetween. By way of example, PCT international application PCT/EP03/03674, published as WO 03/093041 A1, describes embodiments of vehicle roll control stabilizer systems and serves to provide background information related to the present invention.
Referring to FIG. 1, a vehicle 10 is shown schematically and comprises a frame 11 and a pair of front wheels 12 each rotatably mounted on an axle 14, a pair of rear wheels 16 each rotatably mounted on an axle 18, and a shock absorbing system 20 associated with each wheel. A portion 22 of a vehicle roll control system in accordance with the prior art example is associated with the front wheels 12, and a portion 24 of the vehicle roll control system in accordance with the prior art example is associated with the rear wheels 16. The portions 22, 24 are substantially the same but with modifications made to allow fitting to the vehicle 10.
Referring in more detail to FIGS. 2 to 4, the portion 22 of the vehicle roll control system for the front of the vehicle comprises a torsion bar 26, a first arm 28, a second arm 30, a lever arm 32, and a hydraulic actuator 34. The torsion bar 26 is mounted on the vehicle by a pair of resilient mounts 36 in conventional manner to extend longitudinally between the wheels 12. The first arm 28 (FIG. 3) is fixed at one end 38 by a splined connection 40 to the torsion bar 26. The other end 42 of the first arm 28 is connected to the axle 14 of one of the front wheels 12 by a tie rod 43. The second arm 30 (FIG. 4) is rotatably mounted at one end 44 on the torsion bar 26 by way of a bearing 46. The other end 48 of the second arm 30 is connected to the axle 14 of the other front wheel 12 by a tie rod 49. The first and second arms 28, 30 extend substantially parallel to one another when the vehicle is stationary, and substantially perpendicular to the torsion bar 26.
The lever arm 32 (FIG. 4) is fixed at one end 50 to the torsion bar 26 by a splined connection 52 substantially adjacent the one end 44 of the second arm 30 and the bearing 46. The lever arm 32 extends substantially perpendicular to the torsion bar 26 to a free end 54. The hydraulic actuator 34 (FIG. 4) extends between, and is connected to, the free end 54 of the lever arm 32 and the other end 48 of the second arm 30. The hydraulic actuator 34 comprises a housing or outer casing 56, which defines first and second fluid chambers 58, 60 separated by a piston 62, which makes a sealing sliding fit with the housing 56. As shown in FIG. 4, the housing 56 is connected to the other end 48 of the second arm 30, and the piston 62 is connected to the free end 54 of the lever arm 32 by a piston rod 64, which extends through the second fluid chamber (or rod chamber) 60 and is coupled to the piston 62. It will be appreciated that these connections may be reversed. The fluid chambers 58, 60 contain hydraulic fluid and are fluidly connected to fluid lines 66, 68 respectively.
When the piston 62 is moved due to hydraulic forces, the force is transmitted to the rod 64 and lever arm 32. Because the lever arm 32 is rotationally coupled to the torsion bar 26, movement of the piston 62 induces torsion or twisting in the torsion bar 26. The torsion of the torsion bar 26 moves the arms 28, 30 in opposite directions to thereby move the wheels 12 connected thereto in opposite vertical directions. In this manner, the actuator 34 can be operated to provide active stabilization bar control. The portion 24 of the vehicle roll control for the rear of the vehicle is substantially the same as the front portion 22 described above, but with the components (which are shown with prime markings in FIGS. 1 and 2) having a corresponding but different layout.
The hydraulic and electrical control circuit of the vehicle roll control system is shown in FIGS. 5 and 6. The hydraulic circuit includes a fluid pump 80, a fluid reservoir 82, a direction control valve (DCV) 84, a first pressure control valve (PCV-1) 86, and a second pressure control valve (PCV-2) 88. The first pressure control valve 86 has an input fluidly connected to the output of the pump 80 and an output fluidly connected to the input to the second pressure control valve 88. The second pressure control valve 88 has an output fluidly connected to the input to the reservoir 82.
Both of the pressure control valves 86, 88 normally reside in their open position in which fluid flows therethrough. The pressure control valves 86, 88 may both be variable valves in that they can be moved to various partially closed or partially open positions.
The direction control valve 84 has a first port 90 fluidly connected to the output of pump 80; a second port 92 fluidly connected to fluid line 87 connecting the first and second pressure control valves 86, 88; a third port 94 fluidly connected to the fluid line 66 and the first fluid chamber (or piston chamber) 58 of each hydraulic actuator 34, 34′; and a fourth port 96 fluidly connected to the fluid line 68 and the second fluid chamber 60 (or rod chamber) of each hydraulic actuator. The direction control valve 84 is solenoid actuated, and has a closed or de-energized state (FIG. 5) in which the first and second ports 90, 92 are fluidly connected, and the third and fourth ports 94, 96 are isolated from one another and from the other ports, and an energized, actuated or open state (FIG. 6) in which the first port 90 is fluidly connected with the fourth port 96, and in which the second port 92 is fluidly connected with the third port 94.
The pump 80 may be driven by the vehicle engine and hence continuously actuated. Alternatively, the pump 80 may be driven by an electric motor or any other suitable means, either continuously, or variably. The piston or pressure control valves 86, 88 are actuated to adjust the fluid pressure in the hydraulic system between a predetermined minimum pressure and a predetermined maximum pressure, and to adjust the pressure differential between the first and second chambers 58, 60 of each hydraulic actuator 34, 34′ (when the direction control valve 84 is actuated).
The electrical control circuit includes an electronic and/or computerized control module 70. The controller, ECU or control module 70 operates the fluid pump 80, the direction control valve 84, and the pressure control valves 86, 88, when required. The control module 70 actuates the valves 84, 86, 88 dependent on predetermined vehicle conditions which are determined by signals from one or more sensors, such as a pressure sensor 76 (which detects the presence of fluid pressure in the hydraulic circuit), a pressure sensor 77 (which detects the fluid pressure in line 87), a lateral g sensor 74 (which monitors the sideways acceleration of the vehicle), a steering sensor 72 (which monitors the steering angle of the front wheels 12), a vehicle speed sensor 78, and/or any other relevant parameter.
If the control module 70 detects that roll control is required (due, for example, to cornering of the motor vehicle 10), the control module may determine that the module has to generate a force F which acts on the piston rod 64 to extend the actuators 34, 34′ (i.e., to move the pistons 62 up in FIGS. 5 and 6), or to compress the actuators (i.e., move the pistons 62 down in FIGS. 5 and 6), in an axial direction. In particular, when it is desired to move the actuators in compression, pressure control valve 86 is closed (or partially closed) while the pressure control valve 88 and direction control valve 84 are open. In this manner, pressurized fluid flows into the chambers 60 via ports 90, 96 and via line 68. At the same time no (or very little) pressurized fluid flows into the chambers 58. The pressure differential causes the piston rods 64 to move in compression.
In this manner, a pressure which correlates with the force F can be generated and the pressure differential between the first and second chambers 58, 60 varies as the fluid pressure in the second chamber 60 increases or decreases. In other words, assuming no road inputs, the differential pressure between the first chambers 58 and second chambers 60 varies with the position of the piston 62.
For extension, the control module 70 actuates the pressure control valves 86, 88 to provide a predetermined (i.e., equal) fluid pressure in each of the first and second fluid chambers 58, 60, which correlates with the force F, and sets the direction control valve 84 in the actuated position as shown in FIG. 6. In particular, in order to pressurize both of the chamber 58, 60, pressure control valve 88 is closed (or partially closed) while pressure control valve 86 and direction control valve 84 are open. In this manner, pressurized fluid flows into both the chambers 58, 60 via ports 90, 92, 94, 96, and via lines 66, 68. Due to the presence of the piston rods 64, the surface area of the pistons 62 facing the second chambers 60 is less than the surface area of the pistons facing the first chambers 58. Accordingly, when fluid of equal pressure is located in the first and second chambers 58, 60, the pistons 68 move upwardly in extension.
In this case, the pressure differential between the first and second chambers 58, 60 is maintained substantially constant as the level of the fluid pressure increases or decreases as required. In other words, assuming no road inputs, the differential pressure between the first chambers 58 and second chambers 60 remains constant, regardless of the position of the piston 62. When the actuators 34, 34′ are moved in either extension or compression, one of the wheels 12, 16 on an axle 14, 18 is moved upwardly and the other wheel 12, 16 on that same axle 14, 18 is moved downwardly.
A graph illustrating the fluid pressure in the first and second chambers 58, 60 when the actuator 34, 34′ is subjected to a compression force or an extension force is shown in FIG. 14. In this case, the pressurized fluid provided to the chambers 58, 60 is shown as the vertical axis, and the force output by the actuator 34 is shown on the horizontal axis. When the actuator 34 is moved in compression, pressurized fluid is fed to the rod chambers 60, and no pressure or little pressure is present in the piston chambers 58. As the differential pressure is increased (i.e. as one moves to the left side of the graph of FIG. 14) the net output force of the actuator 34 is correspondingly increased.
On the other hand, when the actuator 34 is moved in extension, pressurized fluid of equal pressure is provided in both the rod chamber 60 and piston chamber 58 (the pressure lines for chambers 58, 60 in FIG. 14 are slightly spaced apart for illustrative purposes and to accommodate tolerances in the system). Due to the greater surface area of the piston 62 facing the piston chamber 58, the pressure in chamber 58 acts upon a greater surface area than the pressure in chamber 60, and the actuator 34 is moved in extension.
If the control module 70 detects, for example, that the vehicle is traveling in a straight line and no stabilization bar activation is required, the control module 70 actuates the pressure control valves 86, 88 and the direction control valve 84, and provides small amounts of fluid pressure in the first and second chambers 58, 60 such that the actuators 34, 34′ neither extend nor compress in the axial direction. For example, in this case the DCV valve 84 is open, as are the pressure control valves 86, 88 such that fluid flows freely through the system and does not cause extension or compression of the actuators 34, 34′.
By suitable dimensions for the actuators 34, 34′, the output force from the actuators can be made substantially the same irrespective of the direction of motion of the piston 62. More particularly, the surface area on the side of the pistons 62 facing the rod chambers 60 may be one-half of the surface are of the opposite side of the piston (i.e., the side facing the piston chambers 58). In this manner, if fluid of a predetermined pressure is supplied in both the rod chambers 60 and piston chambers 58, the pistons 62 are moved in extension with a force F. On the other hand, if fluid of the same predetermined pressure is supplied in only the rod chambers 60 then the pistons 62 are moved in compression with the same force F. Thus the particular surfaces areas on the two faces of the pistons 62 help to ensure that the actuators 34, 34′ provide a consistent output force for a given pressure.
In the failure mode, or during certain diagnostics, the direction control valve 84 is de-energized (as shown in FIG. 5) such that the hydraulic actuators 34, 34′ are locked. Fluid can freely flow within the hydraulic system between the pump 80 and the reservoir 82 by way of the first and second ports 90, 92 of the direction control valve 84, and the second pressure control valve 88 (which may include a pressure relief valve). As the third and fourth ports 94, 96 of the direction control valve 84 are closed and isolated, the actuators 34, 34′ are effectively locked since no fluid can flow into or out of the actuator systems.
FIG. 7 shows a first alternative arrangement for the hydraulic circuit in which (in comparison to FIGS. 5 and 6) like parts have been given the same reference numeral. In this first alternative, the direction control valve 84′ has a fifth port 97 fluidly connected to the input of the fluid reservoir 82. In the de-energized state of the direction control valve 84′, the first, second and fifth ports 90, 92, 97 are fluidly connected with each other and to the fluid reservoir 82. In the energized or actuated state of the direction control valve 84′, the fifth port 97 is fluidly isolated from the other ports 90, 92, 94, 96 such that in this mode the system of FIG. 7 operates in generally the same manner as the system of FIGS. 5 and 6.
The presence of the fifth port 97 removes the need for actuation of the second pressure control valve 88 (when the direction control valve 84′ is de-energized), or the presence of a pressure relief for the second pressure control valve. In particular, when the direction control valve 84′ is energized, port 97 provides a direct connection to the reservoir and bypasses the valves 86, 88. Other features and operation of this first alternative hydraulic circuit in a vehicle roll control system are as described above with respect to FIGS. 1 to 6, and 14.
FIG. 8 shows a second alternative arrangement for the hydraulic circuit in which (in comparison to FIGS. 5 and 6) like parts have been given the same reference numeral. In this second alternative, the direction control valve 84 has been split into two parts, a first part 84a (DCV-1) and a second part 84b (DCV-2). The two parts 84a, 84b of the direction valve 84 are actuated separately, but in unison. The first part 84a of the direction control valve 84 incorporates the first port 90, and the fourth port 96 which is fluidly connected with the second fluid chambers 60 of the hydraulic actuators 34, 34′. The second part 84b of the direction control valve 84 incorporates the second port 92, and the third port 94 which is fluidly connected with the first fluid chambers 58 of the hydraulic actuators 34, 34′.
The first part 84a of the direction control valve 84 has an additional port 92′ which is fluidly connected with the second port 92 of the second part 84b. The second part 84b of the direction control valve 84 has an additional port 97 which is fluidly connected with the input of the fluid reservoir 82. In the de-energized state of the first and second parts 84a, 84b of the direction control valve 84, the first port 90 is fluidly connected with the fluid reservoir 82 by way of ports 92′, 92 and 97 as shown in FIG. 8. In the energized state of the first and second parts 84a, 84b of the direction control valve 84, the ports 92′ and 97 are fluidly isolated from the other ports in the same part. The presence of the ports 92′, 97 removes the need for actuation of the second pressure control valve 88 (when the direction control valve 84 is de-energized), or the presence of a pressure relief for the second pressure control valve, particularly when the first and second parts 84a, 84b of the direction control valve are de-energized.
The system of FIG. 8 allows for a zero-net-force condition in the actuators 34, 34′, due to the dual nature of the first and second parts 84a, 84b of the direction control valve. For example, a greater pressure can be applied in the rod chambers 60 than the piston chambers 58. Due to the differing surface area on the two sides of the pistons 62, the pressure differential can be selected to provide a net force of zero upon the pistons 62. This allows the system to continue to push fluid through the actuators 34 without causing extension or compression. Other features and operation of this second alternative hydraulic circuit in a vehicle roll control system are as described above with respect to FIGS. 1 to 6, and 14.
In the prior art example, the direction control valve 84, 84′, 84a and 84b is energized when roll control is required, irrespective of the direction of turn of the vehicle 10. The fluid pressure in the first and second fluid chambers 58, 60 of the hydraulic actuators 34, 34′ is controlled by the selective actuation of one of the first and second pressure control valves 86, 88. By adjusting the actuation of the first and second pressure control valves 86, 88, the hydraulic actuators 34, 34′ are actuated for compression or extension dependent on the direction of turn of the vehicle 10. Consequently, the roll control system controls vehicle roll during a change in the direction of turn of the vehicle by adjusting the operation of the first and second pressure control valves 86, 88. Such an arrangement provides a smooth transition between left and right turns.
The hydraulic system is also applicable for use with a vehicle roll control system, the front portion 122 of which is as shown in FIG. 9 and the rear portion of which is substantially identical to the front portion. In this embodiment in accordance with the prior art example, the front portion 122 comprises a torsion bar 126, a first arm 128, and a hydraulic actuator 134. The first arm 128 is fixed at one end 138 to one end 140 of the torsion bar 126. The other end 142 of the first arm 128 is connected to one of the McPherson struts 120 (commonly referred to as struts). The hydraulic actuator 134 has a piston rod 164, which is fixed to the other end 187 of the torsion bar 126. The housing or outer casing 156 of the actuator 134 is connected to the other strut 120. The hydraulic actuator 134 is substantially the same as the actuator 34 described above with reference to FIGS. 1 to 6, and has a fluid line 166 connected to a first fluid chamber inside the housing, and another fluid line 168 connected to a second fluid chamber inside the housing. The first and second fluid chambers inside the housing 156 are separated by a piston secured to the piston rod 164. The fluid lines 166, 168 for each hydraulic actuator 134 are connected to a hydraulic circuit as shown in FIGS. 5 and 6, which is controlled by a control circuit as shown in FIGS. 5 and 6, or any one of the arrangements shown in FIGS. 7 and 8. The roll control system is operated in substantially the same manner as that described above with reference to FIGS. 1 to 6, and 14, or either one of FIGS. 7 and 8.
The hydraulic system is also applicable for use with a vehicle roll control system as shown in FIG. 10. In this embodiment, the system 222 comprises a torsion bar 226, a first arm 228, a second arm 228′, and a hydraulic actuator 234. The first arm 228 is fixed at one end 238 to one end 240 of the torsion bar 226. The other end 242 of the first arm 228 is connected to one of the shock absorbers 220. The second arm 228′ is fixed at one end 238′ to the other end 287 of the torsion bar 226. The other end 242′ of the second arm 228′ is connected to the other shock absorber 220′. The torsion bar 226 is split into first and second parts 290, 292, respectively. The first and second parts 290, 292 of the torsion bar 226 have portions 294, 296, respectively, which are axially aligned. The axially aligned portions 294, 296 are connected by a hydraulic actuator 234.
The hydraulic actuator 234, as shown in FIG. 11, comprises a cylindrical housing 256 or outer casing, which is connected at one end 239 to the portion 294 of the first part 290 of the torsion bar 226. The actuator 234 further comprises a rod 241 positioned inside the housing 256, extending out of the other end 243 of the housing, and connectable to the portion 296 of the second part 292 of the torsion bar 226. The rod 241 has an external screw thread 249 adjacent the housing 256. Balls 251 are rotatably positioned in hemispherical indentations 253 in the inner surface 255 of the housing 256 adjacent the screw thread 249. The balls 251 extend into the screw thread 249. The rod 241 is slidably and rotatably mounted in the housing 256 at the other end 243 by way of a bearing 259 positioned in the other end 243. This arrangement allows the rod 241 to rotate about its longitudinal axis relative to the housing 256, and to slide in an axial direction A relative to the housing. A piston chamber 261 is defined inside the housing 256. The rod 241 sealingly extends into the piston chamber 261 to define a piston rod 264, and a piston 262 is secured to the end of the piston rod inside the piston chamber. The piston 262 makes a sealing sliding fit with the housing 256 and divides the chamber 261 into a first fluid chamber 258 and a second fluid chamber 260. The first fluid chamber 258 is fluidly connected to fluid line 266, and the second fluid chamber 260 is fluidly connected to fluid line 268.
The fluid lines 266, 268 are connected to a hydraulic circuit as shown in FIGS. 5 and 6, which is controlled by a control circuit as shown in FIGS. 5 and 6, or any one of the arrangements shown in FIGS. 7 and 8. The roll control system 222 is operated in substantially the same manner as that described above with reference to FIGS. 1 to 6, and 14, or any one of FIGS. 7 and 8.
An alternative arrangement for the hydraulic actuator of FIG. 11 is shown in FIG. 12. In this alternative embodiment, the actuator 334 comprises a cylindrical housing 356, which is connected at one end 339 to the portion 294 of the first part 290 of the torsion bar 226. The actuator 334 further comprises a rod 341 positioned inside the housing 356, extending out of the other end 343 of the housing, and connectable to the portion 296 of the second part 292 of the torsion bar 226. The rod 341 has an external screw thread 349 adjacent the housing 356. Balls 351 are rotatably positioned in hemispherical indentations 353 in the inner surface 355 of the housing 356 adjacent the screw thread 349. The balls 351 extend into the screw thread 349. The rod 341 is slidably and rotatably mounted in the housing 356 at the other end 343 of the housing by way of a bearing 359 positioned in the other end. The rod 341 makes a sliding guiding fit with the inner surface 355 of the housing 356 at its end 341′ remote from the second part 292 of the torsion bar 226. This arrangement allows the rod 341 to rotate about its longitudinal axis relative to the housing 356, and to slide in an axial direction A relative to the housing.
First and second fluid chambers 358, 360 are defined inside the housing 356. The rod 341 makes a sealing fit with the inner surface 355 of the housing 356 by way of seal 371 to define a piston 362. The first fluid chamber 358 is positioned on one side of the piston 362, and the second fluid chamber 360 is positioned on the other side of the piston. A seal 369 is positioned adjacent the bearing 359. A portion 364 of the rod 341 defines a piston rod, which extends through the second fluid chamber 360. The first fluid chamber 358 is fluidly connected to fluid line 366, and the second fluid chamber 360 is fluidly connected to fluid line 368. The fluid lines 366, 368 are fluidly connected with one of the hydraulic circuits shown in FIGS. 5 to 8 to actuate the actuator 334.
A further alternative arrangement of hydraulic actuator 334′ is shown in FIG. 13. In this further alternative embodiment, the actuator 334′ is substantially the same as the actuator 334 shown in FIG. 12, but without the sliding guiding fit of the free end 341′ of the rod 341 with the housing 356.
As outlined above, in one arrangement the cross-sectional area of the first fluid chamber of each hydraulic actuator described above is substantially double the cross-sectional area of the piston rod of the hydraulic actuator, when considered on a radial basis. Such an arrangement provides the same output force from the hydraulic actuator in either direction, using the same fluid pressure and equal amounts of fluid.
In the arrangement described above or below, a hydraulic actuator is provided for both the front of the vehicle and the rear of the vehicle, and these hydraulic actuators are controlled in unison. It will be appreciated that the hydraulic actuators may be controlled individually, and in certain cases the portion of the roll control system at the rear of the vehicle may be omitted. Also, the hydraulic actuator for the front of the vehicle may be a different type than the hydraulic actuator for the rear of the vehicle.
In any of the roll control systems described above or below, the hydraulic actuator may include a check valve (not shown, but preferably mounted in the piston) which allows flow of hydraulic fluid from the first fluid chamber to the second fluid chamber only when the fluid pressure in the first fluid chamber is greater than the fluid pressure in the second fluid chamber. With such an arrangement, the second fluid chamber can be connected to a reservoir during servicing of the actuator to bleed air from the hydraulic fluid. Also, the presence of the check valve reduces the risk of air being sucked into the second fluid chamber should the fluid pressure in the second fluid chamber fall below the fluid pressure in the first fluid chamber, and provides further improvements in ride comfort.
When the stabilizer bar is driven or displaced due to external inputs (i.e., a pothole in the road or the like) under normal operating conditions, the movement of the stabilizer bar can, in some cases, cause rapid motion of the pistons in the hydraulic circuit. This rapid movement of the pistons (movement in extension) can cause cavitation in the hydraulic fluid, which results in undesirable performance. Accordingly, there is a need for improved hydraulic circuit for use with a stabilizer bar system.